1. Field of the Invention
The present invention relates to a fluid-filled cylindrical elastic mount which provides a vibration damping effect based on flows of a highly viscous fluid contained therein. This elastic mount may be favorably used as a suspension bushing for an automobile, for example.
2. Discussion of Related Art
As one type of a vibration damper interposed between two members of a vibration system, there is known a fluid-filled cylindrical elastic mount which includes inner and outer metallic sleeves that are connected by a cylindrical elastic body, as disclosed in U.S. Pat. No. 4,883,260 to Kanda, which corresponds to Publication No. 5-47733 of examined Japanese Patent Application. The disclosed elastic mount has a pair of fluid chambers which are formed by closing pockets formed in the elastic body, and which are filled with a fluid having a relatively high viscosity. The elastic mount further includes restricting protrusions formed in the fluid chambers so as to protrude from the inner sleeve toward the outer sleeve, such that restricted portions are formed between the protrusions and the outer sleeve. When a vibrational load is applied between the inner and outer sleeves of the above cylindrical elastic mount, the highly viscous fluid is forced to flow in the restricted portions, so that the mount exhibits a high vibration damping effect based on the viscosity resistance or shearing stress of the viscous fluid.
If the above-described fluid-filled elastic mount is assembled within the highly viscous fluid so as to fill the fluid chambers with the fluid, in the same manner as used for filling a known elastic mount with a low viscosity fluid, a portion of the highly viscous fluid remains on or adheres to the surface of the elastic mount, requiring a cumbersome procedure for removing the fluid afterwards. Accordingly, the filling of the highly viscous fluid is generally effected by injecting the fluid into the fluid chambers through filler inlets, and then sealing or closing the inlets with suitable sealing or closure members, such as blind rivets, as disclosed in the above-identified publication.
In the above case, however, the sealing member closing the inlet protrudes into the corresponding fluid chamber, and the restricting protrusion in the fluid chamber may undesirably abut on the inlet when the elastic mount receives a torsional or twisting load which is applied to the inner and outer sleeves in the circumferential direction. As a result, the sealing member may be damaged due to the abutting contact with the protrusion, resulting in reduced fluid tightness of the mount, or the protrusion may be damaged with a result of deterioration of the vibration damping capability of the mount.
To avoid the above-described problems, the restricting protrusion must be made small-sized so as not to contact with the sealing member. This makes it difficult to ensure a sufficiently large area or volume of the restricted portion formed between the top face or extreme end face of the protrusion and the inner surface of the outer sleeve, and to provide a sufficiently high vibration damping effect based on the fluid flows in the restricted portion. Further, upon application of vibrations to the mount, the contact pressure which acts on unit area of the protrusion upon abutting contact with the outer sleeve is increased with a decrease of the surface area of the top face of the protrusion which defines the restricted portion. This results in reduced durability of the elastic mount.
In the known fluid-filled elastic mount as described above, an intermediate metallic sleeve is generally secured by vulcanization to the outer circumferential surface of the elastic body, and the intermediate sleeve is subjected to a drawing operation so that its diameter is reduced so as to apply preliminary compression to the elastic body to achieve sufficiently high durability of the elastic body. To assure the fluid tightness of the fluid chambers, a sealing rubber layer is interposed between the intermediate sleeve and the outer sleeve.
However, the formation of the sealing rubber layer on the outer circumferential surface of the intermediate sleeve makes it difficult to suitably draw the intermediate sleeve. Therefore, such a sealing rubber layer has to be formed on the inner circumferential surface of the outer sleeve. This necessitates two separate vulcanizing steps to form the elastic body and the sealing rubber layer, respectively, which result in reduced production efficiency of the elastic mount.
In the process of producing the above fluid-filled elastic mount, the pockets formed in the elastic body are open on the outer circumferential surface of the intermediate sleeve, through windows which are formed through the intermediate sleeve such that the windows are aligned with the pockets. It has been found considerably difficult to form these windows in the intermediate sleeve which takes the form of a pipe.